It has long been known from the prior art to produce plastics material containers, and in particular plastic bottles, by plastics material pre-forms first being heated and by the heated plastics material pre-forms then being shaped by means of a shaping device, such as for example a stretch blow moulding machine, to form plastics material containers.
In this case, in addition to rotationally symmetrical containers, oval containers—for example oval PET bottles—are also known from the prior art. In order to produce containers of this type, it is known for the plastics material pre-forms to be heated in a non-uniform manner in the peripheral direction. In addition, however, those containers which are not only made oval but the closure of which must also be screwed onto the opening in the precise rotational setting are also known from the prior art.
This means that even before the shaping procedure the plastics material pre-form has to be orientated with respect to its rotational setting. The problem thus lies in the fact that the oval or asymmetrical containers are frequently not capable of being set and, depending upon the position of the bayonet or thread, they assume an immovable closure position. Only if the plastics material pre-forms are orientated with respect to the bayonet or thread, heated and blow moulded, are the closures then in the position in which they were desired by the customer.
Systems are known from the prior art which have to be constructed in a different manner for every new plastics material pre-form. In addition, the mechanical orientation of the plastics material pre-forms seriously limits the machine performance. It would be possible to use sensors for detection purposes, which are arranged for example in the individual treatment stations of a stretch blow moulding machine. In this case, however, a plurality of sensors would have to be used, namely one sensor for each blow moulding or conveying station, all of which would have to be adjusted and the position of which would also depend upon the plastics material pre-form to be treated in each case.
EP 1 279 477 A1 describes an apparatus and a method of blow moulding bottles. In this case a rotating device is provided which rotates the pre-form on the basis of the signals of a sensor unit in order to arrange it in a specified angular setting in a blow mould in this way.
EP 0 835 736 B1 describes an apparatus for blow moulding and an apparatus for injection stretch blow moulding. In this case rotation devices for rotating the pre-form about its longitudinal axis during the conveying of the pre-form are provided, as well as orientation devices in order to orientate in a pre-set direction the handle projecting from the pre-form.
It may be desirable to provide an apparatus which detects a geometrical position of the plastics material pre-form and, in particular, a rotational position of the plastics material pre-form with respect to its longitudinal axis.